The sewage treatment projects in suburban and rural areas are characterized by small water flow and large number. Due to the high content of organic matter, nitrogen and phosphorus, farmland runoff and wash water from human habitation pressures the environment, and excess nitrogen in drinking water directly threatens human health. The traditional treatment processes in large wastewater treatment plants play an important role, but for small-scale suburban and rural wastewater treatment, the traditional process needs large investment and large area, and is difficult to manage. Therefore, for suburban and rural wastewater treatment, it is necessary to develop a fast and convenient treatment solution.
Biofilm technology is a more popular wastewater treatment method. When the wastewater flows through a biofilm carrier, microorganisms attach to the surface of the carrier, grow and reproduce, and form the biofilm. Due to the contact with air, the surface of the biofilm is dissolved with more dissolved oxygen so as to form aerobic film. The inner layer of the film is dissolved with less oxygen and tends to form an anaerobic layer, and the whole film continues to grow, fall and regenerate. Microorganisms absorb the organic matter in the wastewater as a nutrient in the process of their growth and metabolism, thereby resulting in the degradation of the contaminants.
The traditional biofilm reactor is mostly a single stage reactor. Although it has compact and simple structure, the single stage reactor is not beneficial for the building of the growth environment for the dominant microbial groups with various functions and has a lower processing efficiency. There are also some researches on multi-stage biofilm reactor for wastewater treatment. For example, Chinese invention patent No. 200410013159.3, entitled “carrier circulating biological treating method for sewage treatment”, utility model patent No. 200720022616.4, entitled “multi-dynamic membrane water purification device”, and utility model Patent No. 200820100500.2, entitled “biofilm reactor for wastewater treatment” have disclosed various multi-stage biofilm reactors with different structures. However, the first and the second patent utilize single point intake water, and have the problem of lacking carbon, undesirable nitrogen removal and large quantity of chemical phosphorus removal sludge in the presence of denitrification; while the latter is a horizontal structure, which takes larger space, limits the layer number of biofilm and has a poor moving performance, thus it is not suitable for the portable requirements of rural families. In addition, the above reactors are submerged biofilm reactors, which need aeration to produce aerobic conditions, thus the energy consumption is relative high.